1. Field of the Invention
The invention relates to a grasping method by a grasping apparatus capable of grasping a plurality of types of workpieces of different shapes.
2. Description of Related Art
When handling a plurality of types of workpieces of different shapes with a grasping apparatus that grasps a workpiece or a product or the like, it is troublesome to replace a contact portion, i.e., a portion of the grasping apparatus that directly contacts the workpiece or the like, with a portion corresponding to the shape of each workpiece. Therefore, it has been hoped that a grasping apparatus capable of flexibly handling a variety of types of workpieces having different outer shapes would be developed. Hence, various technologies for grasping apparatuses that are capable of successfully grasping a variety of types of workpieces having different outer shapes have been examined. Japanese Patent Application Publication No. 9-123082 (JP-A-9-123082), for example, described below describes just such a technology.
JP-A-9-123082 describes a grasping apparatus provided with a contact portion capable of handling various outer shapes by encapsulating a large amount of granular substance inside a flexible membrane, and reducing the pressure in the membrane using a vacuum pump or the like, or canceling that pressure reduction. With this grasping apparatus, a contact portion is arranged at a tip end of a support device such as a robotic arm or the like. Also, with a grasping operation by the robotic arm or the like, the contact portion is made to abut against the workpiece or the like and conform to the shape of the workpiece or the like. Then the pressure inside the contact portion is reduced such that the large amount of granular substance inside the membrane is tightly compressed and fixed in place, such that the shape of the contact portion is kept conformed to the shape of the workpiece. Also, with this grasping apparatus, the contact portion is returned to a softened state by canceling the reduced pressure state in the contact portion. Also, using such a grasping apparatus enables the shape of the contact portion to match the outer shapes of various workpieces and the like. As a result, when handling a plurality of various workpieces having different outer shapes, the workpieces can be stably grasped.
Use of a grasping apparatus having this kind of contact portion is premised on the contact portion being deformed to match the outer shape of a workpiece that has already been positioned. A workpiece that is already positioned to match a position specified by the next process is gripped and grasped by the contact portion, and transported.
That is, the shape of the contact portion of this kind of grasping apparatus is not uniform, so the grasping apparatus is not well suited for positioning a workpiece that is not yet positioned. The workpiece is not able to be accurately positioned using only this kind of grasping apparatus.